This invention relates to aviation radios especially those used in general aviation for VOR navigation. The invention specifically relates to NAV/COM transceivers (navigational/ communications) using digital circuitry which circuitry has been configured for low power consumption and for compact size it being incorporated into a hand held unit.
Navigational systems incorporate time and phase shift information in computing distance, bearing and position.
A radio compass is an airborne instrument which operates similarly to a ground direction finder. A sense antenna is an omni-directional type, the signal from which antenna is mixed in the receiver with signal received from the antenna's loop. The radio compass operates on the difference in phas of the induced voltages in a loop and sense antenna outputs provides a cardiod pattern to enable resolution of ambiguity. A cardiod is formed by the additional of the onmi-directional signal to the part of the loop signal with which it is in phase; and the subtraction of the omni-directional signal from the part of the loop signal which it is 180.degree. out of phase. The resulting cardioid antenna pattern has only a single minimum. Only one null position exists for this antenna system. Consequently both direction and sense can be determined from this arrangement.
Omnirange is an azimuth measurement utilizing phase measurement. The signal transmitted by a ground station is formed in such manner that aircraft at different bearings from the station receive distinct information. In affect, the system furnishes the pilot directional guidance by producing definite, descrete courses or paths in space. Radio signals whose characteristics differ as they sweep through 360.degree. are most commonly used for taking bearings in an aircraft system. The aircraft receiver measures the phase difference between two modulation signals on a given carrier. The first signal corresponds to a rotating beam of a becon while the second signal provides the north reference.
A rotating pattern whose phase depends upon its direction at any instant its called the variable phase pattern. A second pattern provides signal reference. The signal is arranged so that at 0.degree. (North) the two signals are in phase, while at other positions of the beam of rotation the variable signal lags behind that of the reference as it covers the 360.degree. of azimuth. At 90.degree. the two signals are 90.degree. out of phase, at a 180.degree. they are 180.degree. out of phase, and so on. The radio equipment in the aircraft measures this phase difference between the reference and the variable signal and thereby determines a positive azimuth reading called "bearing".
V-H-F omnidirectional range (VOR), which is the most commonly employed system, contains a carrier signal which is modulated with a reference signal, which is in turn frequency modulated at a rate of 30 Hz. The time at which the 30 Hz space modulation signal reaches its amplitude peak is depended upon the direction from the station. This signal, when demodulated in an aircraft receiver, results in a 30 Hz voltage, the phase of which is a function of the bearing from the station.
The system is also adjusted so that the positive maximum signal of the amplitude modulated (variable-phase) pattern points to magnetic North at exactly the same instant the frequency modulated (reference-phase) signal reaches its maximum. The circuits within the aircraft receiver compare the phase of the amplitude (space) modulated 30 Hz signal and the voltage recovered from the FM signal modulation. The comparison results in a phase difference directly proportional into 2.degree. of azimuth from the North reference.
A localizer is a vertical plane formed by the radiation of signals from the ground and permits the aircraft to align with the runway centerline during initial approach and descent. This localizer signal includes a number of side bands which enable the aircraft to determine how far it is off the centerline. A modulation method is used which is intended to stablize the alignment of the one course signal with the centerline of the runway. Therefore one side of the centerline has a modulated carrier reference signal and the othe side has a side band signal. With these two signals, the aircraft can determine whether it is off to the left or off to the right of the centerline of the runway. The approach to the runway therefore is defined by the radiation pattern which has a sharp deviation in the side bands creating a null directly along the runway centerline. The radio pattern laid down by a localizing antenna includes a symmetrical pattern about the X-Y axis having a null when approached either from the North or south and a slight dimple when approached either from east or west, wherein the frequency transmitted in each of the quadrants changes, i.e., the first quadrant having a 150 Hz signal and second quadrant having 90 Hz signal and third quadrant having a 150 Hz signal and the fourth quadrant having 90 Hz signal, wherein the North, South, East, West direction are not geographic North, South, East, West, but aligned with the ordinate and axis of a horizontal plot about the centerline of the runway. A very popular type of glide slop is a constant-intesity glide slope. Glide slopes or angles of approach may be generated by antennas putting out parabolic signals, each parabolic envelope having a centerline which may define an angle of approach. A typical glide slope angle is 2.5.degree. which is an angle generally satisfactory for all present day fixed wing aircraft.
One type of glide path indicator is the NULL reference system, wherein the first null of the 150 Hz pattern created by a reference lobe appears at the desired slop angle of 2.5.degree.. In the aircraft's receiver, the 150 Hz output predominates below the glide slope and the 90 Hz output predominates above the glide slope. A distriminator therefore is capable of putting out a signal which can be displayed to the pilot designating whether he is below or above the desired glide path.
The localizer glide slope equipment therefore needs two antennas. One at a slightly different altitude than the second. Energy leaving the first antenna contains equal modulation at 90 and 150 Hz frequencies to serve as a reference signal. Energy leaving the second antenna contains only the side band energy and may be adjusted with respect to the amount of modulated carrier energy.
A navigationsl radial is any one of a number of line of position defined by an azimuth navigational facility. The radial is identified by its bearing (usually the magnetic bearing) "from" the facility. One need merely calculate the supplemental angle (i.e., 360-R where R is the radial bearing from the facility) to find the radial "to" the facility.
General aviation transceivers have in the past utilized specific circuits for specific navigational functions and other specific circuits for sub-functions.
Visher, U.S. Pat. No. 3,581,073 shows an electroinc course line computer. Smith, U.S. Pat. No. 4,184,158 shows a VOR/LOC navigational radio having multiplexed operation. Smith, U.S. Pat. No. 4,215,346 shows a LOC and GS navigational radio. It is understood of course, that "LOC" means localizer signals and "GS" means glide slope signals.
Certain measurements and calculations used in these types of navigational radios are also implemented with specific circuitry. Ferrara, U.S. Pat. No. 4,011,503 shows a phase relation measuring circuit for two signals. Smith, U.S. Pat No. 4,184,157 shows an identification tone reconstitution circuit.
Improved sub-circuits for thes navigational radios have also been developed. McClaskey, U.S. Pat. No. 3,932,821 shows an out of lock detector for a phase lock loop synthesizer.
McClaskey et al U.S. Pat. No. 3,949,296 shows a synthesizer circuit and in U.S. Pat. No. 3,949,305 shows a second synthesizer circuit while in U.S. Pat. No. 3,949,304 shows a fractional megahertz counter for a synthesizer circuit.
Smith, U.S. Pat. No. 4,044,309 shows an automatic squelch circuit for a navigational radio while, Ferrara et al U.S. Pat. No. 4,025,923 shows a synchronous filter circuit for a VOR radio.
All of the above-identified prior art circuits and radios are implemented from descrete components and packaged into the instrument panel of a small airplane.
What is needed is a small, hand held NAV/COM transceiver radio with its own battery pack which can be used as an auxiliary radio or an emergency radio or as the primary radio for light air ballons and experimental/homemade aircraft.
An object of the present invention is to provide a navigational communications VOR transceiver radio of reduced size, being a hand held portable.
A second object is to provide such a radio where certain functions are microprocessor implememted.
A further object is to provide such a radio where signal filtering is custom software implemented.
A further object is to provide such a circuit with redistribution of navigational radio functions between circuitry and between custom software loaded memory accessable to microprocessor components permitting for reduction of circuit size.
An even further object is to implement a navigational seperater decoder circuit utilizing microprocessing circuitry operating under custom software.